Power System Transmission – 100 PYQs

Q1. For a short transmission line, the receiving end voltage is always:
A) Greater than sending end
B) Less than sending end
C) Equal
D) Unpredictable
Ans: B

Q2. Ferranti effect is more pronounced in:
A) Short lines
B) Medium lines
C) Long lightly loaded lines
D) Loaded short lines
Ans: C

Q3. If reflection coefficient = 0, then:
A) No reflection
B) Full reflection
C) Open circuit
D) Short circuit
Ans: A

Q4. Surge impedance loading is maximum for:
A) Short line
B) Medium line
C) Long line
D) Independent of length
Ans: D

Q5. ABCD constants of a transmission line satisfy:
A) AD – BC = 0
B) AD – BC = 1
C) AD + BC = 0
D) AD + BC = 1
Ans: B

Q6. For 220 kV line, corona starting voltage is around:
A) 50 kV
B) 120 kV
C) 180 kV
D) 220 kV
Ans: B

Q7. Shunt compensation in transmission lines is used to:
A) Increase series reactance
B) Improve voltage profile
C) Reduce SIL
D) Reduce power factor
Ans: B

Q8. In bundled conductors, the effective inductance is:
A) Increased
B) Reduced
C) Constant
D) Zero
Ans: B

Q9. Transmission line efficiency increases when:
A) Voltage increases
B) Current decreases
C) Both A and B
D) Resistance increases
Ans: C

Q10. Corona discharge produces:
A) Ozone
B) Radio interference
C) Power loss
D) All of these
Ans: D

Q11. Reflection coefficient for matched load is:
A) +1
B) -1
C) 0
D) ∞
Ans: C

Q12. A 400 kV line with 20 discs in suspension string, the string efficiency is:
A) < 100%
B) 100%
C) > 100%
D) Not defined
Ans: A

Q13. Surge impedance of an overhead line is typically:
A) 100–200 Ω
B) 200–400 Ω
C) 500–800 Ω
D) >1000 Ω
Ans: B

Q14. In transmission lines, which parameter causes charging current?
A) Resistance
B) Inductance
C) Capacitance
D) Leakage
Ans: C

Q15. Kelvin’s law gives:
A) Maximum efficiency condition
B) Economic conductor size
C) Voltage regulation
D) Power transfer
Ans: B

Q16. For maximum power transfer in transmission line:
A) δ = 90°
B) δ = 0°
C) δ = 180°
D) δ = 45°
Ans: A

Q17. Corona loss is more at:
A) High frequency
B) Low frequency
C) Zero frequency
D) DC supply
Ans: A

Q18. String efficiency can be improved by:
A) Increasing number of discs
B) Guard ring
C) Reducing conductor spacing
D) Increasing voltage
Ans: B

Q19. A 132 kV line is classified as:
A) Low voltage
B) Medium voltage
C) High voltage
D) Extra high voltage
Ans: C

Q20. Reflection coefficient at short-circuited line is:
A) +1
B) -1
C) 0
D) ∞
Ans: B

Q21. Surge impedance loading (SIL) is given by:
A) V²/Zc
B) V/Zc
C) V²/R
D) V²/L
Ans: A

Q22. Capacitance grading of cables is done to:
A) Increase corona
B) Reduce dielectric stress
C) Reduce insulation thickness
D) Increase losses
Ans: B

Q23. The power loss due to corona is given by:
A) Peek’s formula
B) Kelvin’s formula
C) Steinmetz formula
D) Maxwell’s law
Ans: A

Q24. In a short transmission line model, which is neglected?
A) R
B) L
C) C
D) X
Ans: C

Q25. The shunt admittance of a transmission line is mainly due to:
A) Line resistance
B) Ground capacitance
C) Inductance
D) None
Ans: B

Q26. Surge impedance is:
A) √(L/C)
B) √(R/L)
C) √(L/R)
D) √(R/C)
Ans: A

Q27. Power transfer capability of a line depends on:
A) Voltage
B) Reactance
C) Load angle
D) All of these
Ans: D

Q28. Transposition of transmission line conductors is done to:
A) Reduce corona
B) Reduce interference with nearby lines
C) Equalize inductance and capacitance
D) Reduce resistance
Ans: C

Q29. Shunt reactors in EHV lines are mainly for:
A) Reactive power absorption
B) Reactive power generation
C) Voltage drop
D) Reduce resistance
Ans: A

Q30. Reflection coefficient magnitude is always:
A) ≤ 1
B) ≥ 1
C) = 0
D) = ∞
Ans: A

Q31. ACSR conductors are preferred because:
A) High strength
B) Less sag
C) Economical
D) All of these
Ans: D

Q32. Ferranti effect is absent in:
A) Short lines
B) Medium lines
C) Long lines
D) EHV lines
Ans: A

Q33. Which insulator is preferred for 400 kV lines?
A) Pin
B) Shackle
C) Suspension
D) Post
Ans: C

Q34. The surge impedance loading of a line increases with:
A) Voltage
B) Length
C) Resistance
D) Frequency
Ans: A

Q35. Radio interference due to corona is minimized by:
A) Bundle conductors
B) Ground wires
C) High resistance
D) Shunt reactors
Ans: A

Q36. The typical range of string efficiency is:
A) 40–50%
B) 60–70%
C) 70–80%
D) 90–100%
Ans: C

Q37. The Ferranti effect occurs because of:
A) Series resistance
B) Series inductance and shunt capacitance
C) Shunt conductance
D) None
Ans: B

Q38. In high-voltage transmission, the most significant line parameter is:
A) R
B) L
C) C
D) G
Ans: C

Q39. A tuned power line is one where:
A) Receiving end voltage = Sending end voltage
B) Power factor is unity
C) No reactive power
D) Line loss = 0
Ans: A

Q40. The corona inception voltage increases with:
A) Decrease in conductor diameter
B) Increase in conductor spacing
C) Increase in air density
D) Both B and C
Ans: D

Q41. For economical transmission, higher voltage is chosen to:
A) Reduce current
B) Reduce losses
C) Reduce conductor size
D) All of these
Ans: D

Q42. In cables, dielectric loss is proportional to:
A) f
B) f²
C) 1/f
D) √f
Ans: A

Q43. When a transmission line is terminated in its surge impedance:
A) No reflection
B) Full reflection
C) Maximum reflection
D) Zero transmission
Ans: A

Q44. Which tower is used for angle location in transmission lines?
A) Suspension tower
B) Tension tower
C) Guyed tower
D) None
Ans: B

Q45. Skin effect in conductors increases with:
A) Decreasing frequency
B) Increasing frequency
C) Decreasing diameter
D) None
Ans: B

Q46. In a cable, the maximum stress occurs at:
A) Conductor surface
B) Outer sheath
C) Mid-point of dielectric
D) Neutral point
Ans: A

Q47. String insulator units are connected in:
A) Series
B) Parallel
C) Both series & parallel
D) Star
Ans: A

Q48. For overhead lines, the most economical conductor shape is:
A) Square
B) Hollow
C) Circular
D) Hexagonal
Ans: C

Q49. When transmission line length increases, Ferranti effect:
A) Decreases
B) Increases
C) Remains constant
D) Zero
Ans: B

Q50. In AC transmission, efficiency increases by:
A) Increasing voltage
B) Reducing losses
C) Power factor correction
D) All of these
Ans: D

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Q51. Which conductor arrangement reduces corona loss?
A) Single
B) Bundled
C) Twin
D) None
Ans: B

Q52. For 11 kV line, the insulator type used is:
A) Pin
B) Suspension
C) Shackle
D) Post
Ans: A

Q53. Which factor does not affect corona loss?
A) Frequency
B) Conductor surface condition
C) Current magnitude
D) Air density
Ans: C

Q54. In EHV cables, the main limitation is:
A) Corona
B) Charging current
C) Skin effect
D) Radio interference
Ans: B

Q55. Voltage regulation is negative due to:
A) Ferranti effect
B) Corona
C) Shunt reactor
D) Skin effect
Ans: A

Q56. The typical span of a transmission line tower is:
A) 10 m
B) 20 m
C) 300–400 m
D) 2000 m
Ans: C

Q57. Which factor improves string efficiency?
A) High capacitance between discs
B) Guard ring
C) Low conductor spacing
D) Increase in leakage current
Ans: B

Q58. Which transmission is more economical for long distance?
A) AC
B) DC
C) Both equal
D) None
Ans: B

Q59. Sag in a conductor increases with:
A) Decrease in span
B) Increase in temperature
C) Decrease in temperature
D) Decrease in weight
Ans: B

Q60. The safe limit of sag is governed by:
A) Tension
B) Clearance
C) Both A and B
D) None
Ans: C

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Q61. Ferranti effect is due to:
A) Series inductance and shunt capacitance
B) Shunt resistance
C) Line losses
D) Sag
Ans: A

Q62. If sending end power factor = unity, the receiving end power factor of a short line will be:
A) Unity
B) Lagging
C) Leading
D) Zero
Ans: B

Q63. The critical disruptive voltage depends on:
A) Air density
B) Surface condition
C) Conductor diameter
D) All of these
Ans: D

Q64. Ferranti effect is more serious in:
A) Loaded lines
B) Lightly loaded lines
C) Cables
D) Transformers
Ans: B

Q65. Transmission line constant "C" is called:
A) Series impedance
B) Shunt admittance
C) Transfer constant
D) Propagation constant
Ans: B

Q66. Which parameter is neglected in a short line model?
A) Resistance
B) Reactance
C) Capacitance
D) Inductance
Ans: C

Q67. In DC transmission, which loss is absent?
A) Copper
B) Skin effect
C) Corona
D) None
Ans: B

Q68. The dielectric strength of air is approximately:
A) 1 kV/cm
B) 30 kV/cm
C) 100 kV/cm
D) 3 kV/cm
Ans: B

Q69. Reflection coefficient at open circuit =
A) +1
B) -1
C) 0
D) None
Ans: A

Q70. Critical disruptive voltage increases with:
A) Temperature rise
B) Decrease in air density
C) Increase in conductor diameter
D) Decrease in conductor spacing
Ans: C

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Q71. SIL of a line is proportional to:
A) V
B) V²
C) 1/V
D) 1/V²
Ans: B

Q72. The efficiency of a transmission line mainly depends on:
A) Voltage
B) Current
C) Power factor
D) Resistance
Ans: A

Q73. Surge impedance of cable is:
A) Higher than overhead line
B) Lower than overhead line
C) Same
D) Infinite
Ans: B

Q74. Overhead lines are transposed to:
A) Reduce corona
B) Reduce interference with communication lines
C) Reduce resistance
D) Increase sag
Ans: B

Q75. The propagation constant of a line is:
A) √(YZ)
B) √(Z/Y)
C) Z/Y
D) Y/Z
Ans: A

Q76. The attenuation constant of a line represents:
A) Losses
B) Surge impedance
C) Velocity
D) Phase shift
Ans: A

Q77. String efficiency always:
A) Increases with number of discs
B) Decreases with number of discs
C) Remains constant
D) Independent
Ans: B

Q78. An ACSR conductor has:
A) Steel core with aluminium strands
B) Aluminium core with steel strands
C) Copper with aluminium strands
D) None
Ans: A

Q79. Sag is proportional to:
A) Span²
B) Span
C) 1/Span
D) √Span
Ans: A

Q80. For an overhead line, inductance depends upon:
A) Length
B) Spacing
C) Radius
D) All of these
Ans: D

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Q81. Ferranti effect is mainly due to:
A) Shunt capacitance
B) Resistance
C) Inductance
D) Ground wires
Ans: A

Q82. Surge impedance is independent of:
A) Frequency
B) Inductance
C) Capacitance
D) Line length
Ans: D

Q83. The dielectric stress in cables is maximum at:
A) Core conductor
B) Sheath
C) Mid-point
D) Insulation surface
Ans: A

Q84. The critical voltage gradient for corona is reduced by:
A) Increasing conductor diameter
B) Reducing spacing
C) Using rough surface conductors
D) Increasing air density
Ans: C

Q85. Which line requires shunt reactors?
A) Short
B) Medium
C) Long
D) All
Ans: C

Q86. Ferranti effect is absent in:
A) DC lines
B) AC lines
C) Both
D) None
Ans: A

Q87. A line is called tuned when:
A) Length = λ/4
B) Length = λ/2
C) Length = λ
D) None
Ans: B

Q88. The surge impedance of a line is independent of:
A) Line length
B) Line constants
C) Frequency
D) Both A and C
Ans: D

Q89. Which tower is lightest?
A) Suspension
B) Tension
C) Terminal
D) None
Ans: A

Q90. Shunt capacitors are used for:
A) Leading VARs
B) Lagging VARs
C) Voltage drop
D) None
Ans: A

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Q91. The Ferranti effect magnitude increases with:
A) Decrease in frequency
B) Increase in frequency
C) Decrease in length
D) None
Ans: B

Q92. The surge impedance of overhead line is about:
A) 100 Ω
B) 300–400 Ω
C) 800 Ω
D) 1000 Ω
Ans: B

Q93. The ABCD constants are used in:
A) Transmission line modeling
B) Transformers
C) Generators
D) Circuit breakers
Ans: A

Q94. Maximum power transfer in a line occurs when:
A) Line reactance = 0
B) Load angle = 90°
C) Voltage = maximum
D) None
Ans: B

Q95. Shunt reactors are connected at:
A) Sending end
B) Receiving end
C) Both ends
D) Middle
Ans: C

Q96. Insulator flashover voltage is always:
A) Greater than puncture voltage
B) Less than puncture voltage
C) Equal
D) None
Ans: B

Q97. The sag is inversely proportional to:
A) Conductor tension
B) Span²
C) Span
D) None
Ans: A

Q98. For same voltage, corona loss is more in:
A) AC
B) DC
C) Equal
D) None
Ans: A

Q99. The bundle conductor spacing is decided by:
A) Corona effect
B) Skin effect
C) Inductance
D) Capacitance
Ans: A

Q100. In a long line, receiving end voltage is higher due to:
A) Ferranti effect
B) Skin effect
C) Line losses
D) None
Ans: A